Iran has released four American prisoners, including a Washington Post reporter, a Christian pastor and a former U.S. Marine, Iranian television said on Saturday.

A fifth American, student Matthew Trevithick, was also released, a U.S. official said, separately from the four other Americans. It was unclear when Trevithick, a student, was released.

The move came ahead of the expected lifting of international sanctions on Iran later on Saturday as part of a landmark deal between major powers and Iran to curb Tehran's nuclear program.

The Americans released included Jason Rezaian, the Washington Post's Tehran correspondent, Saeed Abedini, a pastor from Idaho, Amir Hekmati, a former Marine from Flint, Michigan, and Nosratollah Khosravi, state television said.

A report by the semi-official ISNA news agency quotes a statement from the Tehran prosecutor's office as saying the inmates were freed "within the framework of exchanging prisoners." In exchange for the four prisoners, the U.S. will release seven Iranian-Americans it had jailed, the Islamic Republic's official IRNA news agency reported.

"Prosecutor Abbas Jaafari told IRNA that four dual nationality Iranian-American prisoners, passing prison terms in Iran, will be exchanged with seven Iranian nationals languishing at the U.S. jails," it reported.

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It said the swap included a clause under which the United States would no longer pursue the extradition of 14 Iranians for alleged involvement in purchasing arms in the United States for supply to Iran.

U.S. officials confirmed the announcement, adding that the case of Iranian-American businessman Siamak Namazi, also jailed in Iran, was not yet resolved. The United States has offered clemency to seven Iranians, six of whom held dual U.S.-Iranian citizenship, who were convicted or were facing trial in the United States, a U.S. official said.

Iranian Foreign Minister Mohammad Javad Zarif, in Vienna to meet U.S. Secretary of State John Kerry, spoke cryptically of a possible negotiation.

But the family of one of the U.S prisoners received unofficial word from Iran that their relative was being released today, according to a person close to that family who spoke on condition the family not be identified.

Washington Post reporter Rezaian, 39, was arrested in July 2014 along with three other journalists, including his wife Yeganeh Salehi. All were freed except for Rezaian, an Iranian-American who was convicted in a closed-door trial for espionage and other offenses including "collaborating with hostile governments." The U.S. State Department called the charges "absurd."

A Washington Post spokeswoman said the newspaper had not yet received official confirmation of Rezaian's release.

Former Marine Hekmati, 32, was detained while visiting an Iranian relative in August 2011 and sentenced to death for espionage. He was re-sentenced to 10 years in jail in 2013 after the death sentence was overturned. Abedini, a 35-year-old American Christian pastor born in Iran, was sentenced to eight years in prison in 2013 on charges of attempting to undermine the Iranian government.

The inclusion of Nosratollah Khosravi on the list came as a surprise and there were no biographical details about him immediately available.

Separately, Robert Levinson disappeared in Iran in 2007 while working for the CIA on an unapproved intelligence mission. American officials are unsure if the former FBI agent is even still alive. Iranian officials deny knowing where he is. Levinson traveled to Kish island and checked into hotel, purportedly investigating cigarette smuggling. He met U.S. fugitive Dawud Salahuddin, the last man known to see him. The CIA family paid Levinson's family over $2 million and some staffers lost their jobs over his unauthorized work. A proof of life video surfaced in 2011, saying he was held by a group. His family received photos that year, too, of Levinson bearded, shackled, wearing orange jumpsuit and holding signs in broken English. He has seven children. He suffers from diabetes and high blood pressure.

The Obama administration says the Americans come up in every conversation with the Iranians.

U.S. Secretary of State John Kerry will join Federica Mogherini of the European Union and Iranian Foreign Minister Mohammad Javad Zarif in Vienna, the headquarters of the UN's International Atomic Energy Agency, later Saturday.

IAEA certification that Iran is honoring its obligations would trigger sanctions relief for Iran worth an estimated $100 billion.

Under the July 14 deal between Iran and six world powers, Tehran Iran agreed to crimp programs it could use to make nuclear weapons in return for an end to international nuclear-related sanctions

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